W42C32-05 Spread Spectrum Frequency Timing Generator Features Key Specifications • Maximized EMI suppression using Cypress’s Spread Spectrum technology • Generates a spread spectrum timing signal • Reduces measured EMI by as much as 12 dB • Integrated loop filter components • Requires a single low-cost fundamental crystal (or other frequency reference) for proper operation • Special spread spectrum control functions • Low-power CMOS design • Available in 16-pin SOIC package, (300 mil) Cycle-to-Cycle Jitter .................................................... 250 ps 45/55 Duty Cycle .................................... approximately 1.4V Selectable Frequency spread 2 ns rise/fall time 0.4V to 2.0V, 3.3V supply 2 ns rise/fall time 0.8V to 2.4V, 5.0V supply Table 1. Frequency Spread Selection W42C32-05 Overview The W42C32 modulates the output of a single PLL in order to ‘spread’ the bandwidth of a synthesized clock and, more importantly, decrease the peak amplitudes of its fundamental harmonics. Since peak amplitudes are reduced, the radiated electromagnetic emissions of the W42C32-05 are significantly lower than the typical narrow band signal produced by oscillators and most frequency generators. Lowering a signal’s amplitude by increasing its bandwidth is a method of reducing EMI called ‘spread spectrum frequency timing generation’. This patented technique not only reduces the emissions of the primary clock, but also impacts every signal synchronized to it. FS2 FS1 FS0 REFOUT (MHz) CLKOUT (MHz) VDD (V) 0 0 0 22.1148 44.2296 ± 2.5% 5.0 0 0 1 22.1148 44.2296 ±1.5% 5.0 0 1 0 14.7456 29.4912 ± 2.5% 5.0 0 1 1 18.432 18.432 ± 2.5% 5.0 1 0 0 14.318 66.66 – 2% 3.3 1 0 1 1 1 0 1 1 1 Reserved 14.318 100 – 2% Reserved 3.3 3.3 3.3 Pin Configuration SOIC Cypress Semiconductor Corporation • 1 2 3 4 5 6 7 8 W42C32-05 PD# X1 X2 GND AGND FS0 TEST CLKOUT REFOUT FS2 FS1 SSON# RESET VDD AVDD REFEN# 16 15 14 13 12 11 10 9 3901 North First Street • San Jose • CA 95134 • 408-943-2600 September 28, 1999, rev. ** W42C32-05 Pin Definitions Pin No. Pin Type CLKOUT 8 O Pin Name Pin Description Output Modulated Frequency: Frequency is set using FS0:2 (refer to Table 1). REFOUT 16 O Reference Output: A buffered version of the input frequency. X1 2 I Crystal Connection or External Reference Frequency Input: This pin has dual functions. It can be used as either an external crystal connection, or as an external reference frequency input. X2 3 I Crystal Connection: If using an external reference, this pin must be left unconnected. SSON# 13 I Spread Spectrum Control (active LOW): Pulling this input signal HIGH turns the internal modulating waveform off. This pin has an internal pull-down resistor. FS0 6 I Frequency Selection Bit 0: This pin selects the frequency and spreading characteristics. Refer to Table 1. This pin has an internal pull-up resistor. FS1 14 I Frequency Selection Bit 1: This pin selects the frequency and spreading characteristics. Refer to Table 1. This pin has an internal pull-up resistor. FS2 15 I Frequency Selection Bit 2: This pin selects the frequency and spreading characteristics. Refer to Table 1 (note the VDD specification). This pin has an internal pull-up resistor. PD# 1 I Power-down (active LOW): Enabling power-down reduces current consumption and disables the clock outputs. This pin has an internal pull-up resistor. REFEN# 9 I Reference Clock Selection Input: Pulling this signal LOW turns the REFOUT clock output on. This pin has an internal pull-up resistor. RESET 12 I Reset: A reset starts the spread spectrum modulating frequency at the beginning point of the modulation profile. This pin has an internal pull-down resistor. To reset the spread spectrum modulating frequency, pull this pin from LOW to HIGH. VDD 11 P Power Connection: Connected to either 3.3V or 5.0V power supply. VDD and AVDD must be the same voltage level. AVDD 10 P Analog Power Connection: Connected to either 3.3V or 5.0V power supply. VDD and AVDD must be the same voltage level. GND 4 G Ground Connection: Connect to the common system ground plane. AGND 5 G Analog Ground Connection: Connect to the common system ground plane. TEST 7 I Three-state Input: Pulling this input pin and REFEN# pin HIGH, CLKOUT will be three-stated. This pin has an internal pull-down resistor. Notes: 1. Pull-up resistors not CMOS level. 2. Pulling PD# and REFEN# input pins HIGH, REFOUT will be three-stated. 2 W42C32-05 Using frequency select bits (FS2:0 pins), various spreading percentages for different input frequency ranges can be chosen. For example, refer to the W42C32-05 in Table 1. If the logic level on FS2:0 = 000, then an input reference frequency between 14 and 24 MHz will produce an output frequency at twice the reference frequency with a spread of ±2.5%. Functional Description The W42C32-05 uses a phase-locked loop (PLL) to multiply the frequency of a low-cost, low-frequency crystal up to the desired clock frequency. The basic circuit topology is shown in Figure 1. An on-chip crystal driver causes the crystal to oscillate at its fundamental. The resulting reference signal is divided by Q and fed to the phase detector. The VCO output is divided by P and also fed back to the phase detector. The PLL will force the frequency of the VCO output signal to change until the divided output signal and the divided reference signal match at the phase detector input. The output frequency is then equal to the ratio of P/Q times the reference frequency. The unique feature of the Spread Spectrum Frequency Timing Generator is that a modulating waveform is superimposed at the input to the VCO. This causes the VCO output to be slowly swept across a predetermined frequency band. A larger spreading percentage improves EMI reduction. However, large spread percentages may either exceed system maximum frequency ratings or lower the average frequency to a point where performance is affected. For these reasons, spreading percentages between ±0.875% and ±2.5% are most common. Additional Features of the W42C32-05 A RESET pin is available to aid in applications which have multiple PLL clock generators. When a reset is issued, the modulation profile shown in Figure 3 is reset to its starting point. This feature is necessary for applications in which two spread spectrum systems must synchronize with each other. Because the modulating frequency is typically 1000 times slower than the fundamental clock, the spread spectrum process has little impact on system performance. The REFOUT out pin provides a buffered version of the input clock frequency. Frequency Selection With SSFTG The SSON# pin disables the spread spectrum function when set to logic HIGH. Otherwise, an internal pull-down resistor leaves this feature enabled. In Spread Spectrum frequency timing generation, EMI reduction depends on the shape, modulation percentage, and frequency of the modulating waveform. While the shape and frequency of the modulating waveform in the W42C32 are fixed, the modulation percentage may be varied. The PD# pin reduces power consumption and disables the clock outputs when set to logic LOW. Otherwise, an internal pull-up resistor places the W42C32-05 into normal mode. VDD X1 CLKOUT XTAL X2 Freq. Divider Q Phase Detector Charge Pump Σ VCO Post Dividers Modulating Waveform Crystal load capacitors as needed Feedback Divider P PLL GND Figure 1. System Block Diagram (Concept, not actual implementation) 3 W42C32-05 Spread Spectrum Frequency Timing Generation 5dB/div The benefits of using Spread Spectrum Frequency Timing Generation are depicted in Figure 2. An EMI emission profile of a clock harmonic is shown. SSFTG Amplitude (dB) Contrast the typical clock EMI with the Cypress spread spectrum clock. Notice the spike in the typical clock. This spike can make systems fail quasi-peak EMI testing. The FCC and other regulatory agencies test for peak emissions. With Cypress’s Spread Spectrum Frequency Timing Generator (SSFTG), the peak energy is much lower (at least 8 dB) because the energy is spread out across a wider bandwidth. Typical Clock Modulating Waveform The shape of the modulating waveform is critical to EMI reduction. The modulation scheme used to accomplish the maximum reduction in EMI is shown in Figure 3. The period of the modulation is shown as a percentage of the period length along the X axis. The amount that the frequency is varied is shown along the Y axis, also shown as a percentage of the total frequency spread. Cypress frequency selection tables express the modulation percentage in two ways. The first method displays the spreading frequency band as a percent of the programmed average output frequency, symmetric about the programmed average frequency. This method is always shown using the expression fCenter ± XMOD% in the frequency spread selection table. Figure 2. Typical Clock and SSFTG Comparison Time Figure 3. Modulation Waveform Profile 4 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 100% 90% 80% 70% 60% 50% 40% 30% 20% 100% 80% 60% 40% 20% 0% –20% –40% –60% –80% –100% 10% Frequency Shift The second approach is to specify the maximum operating frequency and the spreading band as a percentage of this frequency. The output signal is swept from the lower edge of the band to the maximum frequency. The expression for this approach is fMAX – XMOD%. Whenever this expression is used, Cypress has taken care to ensure that fMAX will never be exceeded. This is important in applications where the clock drives components with tight maximum clock speed specifications. W42C32-05 Absolute Maximum Ratings above those specified in the operating sections of this specification is not implied. Maximum conditions for extended periods may affect reliability. Stresses greater than those listed in this table may cause permanent damage to the device. These represent a stress rating only. Operation of the device at these or any other conditions Parameter Description Rating Unit V VDD, VIN Voltage on any pin with respect to GND –0.5 to +7.0 –65 to +150 °C 0 to +70 °C –55 to +125 °C TSTG Storage Temperature TA Operating Temperature TB Ambient Temperature under Bias DC Electrical Characteristics: 0°C < TA < 70°C, VDD = 5.0V±10%, 3.3V±5% Parameter Description Test Condition Min Max Unit 35 45 mA 4 cycles IDD Supply Current tOFF Power Down Time tON Power Up Time First locked clock cycle after PD# goes HIGH 5 ms tEN Enable/Disable Time Time required for output to be enabled/disabled 4 cycles VIL Input Low Voltage VDD = 5.0V 0.8 V VDD = 3.3V 0.15VDD V VIH Input High Voltage VDD = 5.0, 100 MHz Typ VDD = 5.0V 3.0 V VDD = 3.3V 0.7VDD V VOL Output Low Voltage VOH Output High Voltage IIL Input Low Current –100 µA IIH Input High Current 10 µA IOL Output Low Current IOH CI 0.4 VDD = 5.0V 2.4 VDD = 3.3V 2.4 V V V @ 0.4V, VDD = 3.3V 2.4 Output High Current @ 2.4V, VDD = 3.3V 2.4 Input Capacitance All pins except X1, X2 7 pF CL XTAL Load Capacitance Pins X1, X2 16 pF RP Input Pull-Up Resistor VIN = 0V 300 kΩ ZOUT Clock Output Impedance Any clock output pin 33 Ω Note: 3. Cycle refers to input clock cycles supplied by the input crystal or reference. 5 mA mA W42C32-05 AC Electrical Characteristics: TA = 0°C to +70°C, VDD = 5V±10%. 3.3V±5% Symbol Parameter Test Condition Min Typ Max Unit fIN Input Frequency 12 28 MHz fOUT Output Frequency 18 100 MHz tR Output Rise Time 15-pF load 0.4V–2.4V 1 2 ns tF Output Fall Time 15-pF load 2.4V–0.8V 1 2 ns tOD Output Duty Cycle 15-pF load, V DD = 5.0V 45 55 % tOD Output Duty Cycle 15-pF load, V DD = 3.3V 40 60 % tID Input Duty Cycle 40 60 % tJCYC Jitter, Cycle-to-Cycle 300 ps Harmonic Reduction 250 fin = 16 MHz, ninth harmonic measured, reference board, 15-pF load 6 8 dB W42C32-05 The 10-µF decoupling capacitor shown should be a tantalum type. For further EMI protection, the VDD connection can be made via a ferrite bead, as shown. Application Information Recommended Circuit Configuration The 16-pF XTAL load capacitors can be used to raise the integrated 12-pF capacitors up to a total load of 20 pF on the crystal. For optimum performance in system applications the power supply decoupling scheme shown in Figure 4 should be used. VDD decoupling is important to both reduce phase jitter and EMI radiation. The 0.1-µF decoupling capacitor should be placed as close to the VDD pin as possible, otherwise the increased trace inductance will negate its decoupling capability. Recommended Board Layout Figure 4 shows a recommended 2-layer board layout. 1 16 2 15 3 14 4 G 13 5 G 12 6 11 7 10 8 9 XTAL1 C2 = 16 pF Ground 33Ω CLKOUT REFOUT 33Ω C1 =16 pF C5 G (Via to ground plane) C6 G Voltage Supply Input (3.3V, 5.0V) Ferrite Bead (Modulated Output) C1, C2 = XTAL load capacitors. Typical value is 16 pF. C3, C5, C6 = High frequency supply decoupling capacitor (0.1-µF recommended). C3 = 0.1 µF C4 = Common supply low frequency decoupling capacitor (10-µF tantalum recommended). 33Ω = Match value to line impedance. C4 = 10 µF Ground Figure 4. Recommended Board Layout (2-Layer Board) Ordering Information Ordering Code W42C32 Freq. Mask Code Package Name 05 G Package Type 16-pin Plastic SOIC (300-mil) Document #: 38-00808 7 W42C32-05 Package Diagram 16-Pin Small Outline Integrated Circuit (SOIC, 300-mil) © Cypress Semiconductor Corporation, 1999. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress Semiconductor product. Nor does it convey or imply any license under patent or other rights. Cypress Semiconductor does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress Semiconductor products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress Semiconductor against all charges.